Low shrink thermosetting polyesters

ABSTRACT

This invention pertains to a one-component, low shrink molding resin system comprising a thermoplastic, branched alkyd in combination with a thermosetting dicyclopentadiene modified polyester resin. The low shrink molding resin systems are stabilized dispersions wherein the branched thermoplastic alkyd is dispersed within the dicyclopentadiene polyester resin (polyester polymer + monomer) to provide a uniform dispersion. The low shrink molding resin system can be thickened with alkaline earth and/or hydroxide thickeners suitable for use in low shrink molding compositions for producing low-profile molded parts.

BACKGROUND OF THE INVENTION

This application pertains to low shrink molding resin systems andrelates to commonly assigned and allowed application identified as Ser.No. 330,474 filed Feb. 8, 1973, now U.S. Pat. No. 3,883,612, issued May13, 1975 and said application is incorporated herein by reference.

Unsaturated polyester polymers blended with vinyl monomers such asstyrene are well-known molding resins that can be cured at roomtemperature or under heat and/or pressure to form a thermoset plasticmolded part. These molding resins often are combined with inert fillers,glass fibers, glass flakes, talcs, and the like for the purpose ofobtaining improved impact strength, flexural strength, and rigidity inmolded parts. Most conventional thermosetting resins, however,characteristically shrink about 8% to 10% by volume and consequentlydistort during the molding process whereby the shrinkage thereof isunsatisfactory despite the many favorable inherent characteristics ofpolyester molding compositions. To offset the shrinkage characteristic,resin systems have been suggested based primarily on a resin system of athermosetting polyester polymer, a thermoplastic addition polymer, and areactive ethylenically unsaturated monomer.

A particularly desirable low shrink resin composition is a stabilizedone-component system disclosed in Ser. No. 330,474 filed Feb. 8, 1973,and copending herewith which provides a dicyclopentadiene-modifiedpolyester resin intermixed primarily with a modified acrylicthermoplastic polymer having acid functionality.

It now has been found that an improved low shrink thermosettingpolyester resin system can be achieved by dispersing a thermoplastic,branched, fatty acid modified alkyd dispersed within adicyclopentadiene-modified polyester resin to produce a stabilized,uniform dispersion mixture.

SUMMARY OF THE INVENTION

In accordance with this invention, the thermosetting low shrink moldingresin composition comprises a branched, fatty acid modifiedthermoplastic alkyd polymer mixed with a dicyclopentadiene-modifiedunsaturated polyester polymer and a reactive monomer to provide auniform stabilized resin dispersion mixture. The branched, fatty acidalkyd is a thermoplastic short oil alkyd containing by weight betweenabout 4% to 20% saturated fatty acid and at least an equivalent molaramount of polyol to provide a branched alkyd polymer having a branchingfunctionality greater than 2.

DETAILED DESCRIPTION OF THE INVENTION

The low shrink resin molding composition of this invention comprises abranched fatty acid modified alkyd polymer dispersed within adicyclopentadiene-modified unsaturated polyester and a reactivecopolymerizable monomer.

In accordance with this invention, the branched fatty acid modifiedthermoplastic alkyd polymers are copolymers of diols and minor amountsof polyols esterified with dicarboxylic acids and monocarboxylicsaturated fatty acids to provide a branched alkyd containing betweenabout 4% to 20% by weight fatty acid. The diols are conventional glycolsand include for example ethylene glycol, propylene glycol, dipropyleneglycol which can be combined with minor amounts of higher glycols suchas 1,3 and 1,4 butylene glycol, 1,4 cyclohexanedimethanol. The polyolscontain three or more reactive hydroxyl groups and include, for example,glycerol, pentaerythritol, dipentaerythritol, and trimethylol propaneand trimethylol ethane. Trimethylol propane is the most preferred polyoldue to the three primary alcohol groups which have equivalent reactivityas compared to glycerol which has a less reactive secondary polyolgroup. The triols can be combined with minor amounts of higher polyolsprovided that sufficient monocarboxylic fatty acid is used to terminatethe polymer chain and avoid gellation. The most preferred polyols aretrimethylol propane and trimethylol ethane and will comprise a majorportion of the polyol. The average equivalent hydroxyl functionality ofthe diols and the polyols in the branched alkyd is greater than 2.0 andcan be as high as 2.3 although the desired average equivalent hydroxylfunctionality is between about 2.02 and 2.2. The preferred equivalentsrange is between about 2.04 and 2.16. The average hydroxyl equivalentfunctionality of the alkyd is figured on the basis that glycolequivalent functionality is 2.0 and that a triol hydroxyl equivalentfunctionality is 3.0. The equivalent hydroxyl functionality is figuredempirically by assigning a hydroxyl functionality of 2 to glycol and 3to triol and then figuring the average hydroxyl equivalency. Forexample, an alkyd containing 0.08 moles of triol such as trimethylpropane and 0.92 moles of diol such as propylene glycol is figuredempirically to have 2.0 equivalents of linear polymerization and 0.08equivalent of branching to produce an equivalent functionality of 2.08and consequently a branched polymer. The polyol functionality is figuredempirically since in practice a portion of the monocarboxylic acidesterifies a portion of the 0.08 equivalents of the triol but not allthus assuring branched alkyd polymer.

In accordance with this invention, the diols and polyols arepreferentially esterified with saturated dicarboxylic acids whichinclude, for example, succinic acid, glutaric acid, adipic, acid,sebacic acid, pimelic acid, suberic acid, azelaic, and like saturateddicarboxylic acids having between about 4 to 10 carbon atoms whereinadipic, azelaic, and sebacic are the most common and are preferred. Thediols and polyols are further esterified with monocarboxylic fatty acidwhich include, for example, lauric acid, palmitic acid, myristic acidand stearic acid. The branched alkyd contains by weight between about 4%to 20% monocarboxylic fatty acid being substantially free of conjugateddouble bonds and preferably substantially saturated monocarboxylicacids. The moles of monocarboxylic fatty acid are less than or equal tothe moles of polyol to provide some branching which occurs even thoughequivalent molar amounts of monocarboxylic fatty acid are availablesince a portion thereof esterifies the glycol whereby the polyol such asa triol is esterified by dicarboxylic acid and thus provides polymerbranching. Branching in the alkyd is produced by providing that theaverage polyol functionality is greater than 2 and preferably betweenabout 2.02 and 2.2. Trimethylol propane and trimethylol ethane arepreferred triols which have primary alcohol groups which tend to reactat equivalent rates.

In practice, preferably all of the glycol and polyol requirements can becharged to the reactor and reacted together with the full acid chargeexcept for the monocarboxylic acid which is added later in the cookafter about 75% of the available dicarboxylic acid groups have beenesterified. Thus, the polyol is first reacted with dicarboxylic acid toinsure preferential reaction and branching with the triol. In contrast,a conventional alkyd derived from an equivalent oil such as coconut oilproduces alkyds having a wide molecular weight range which tends toprovide an unstable mixture upon being mixed with the DCP-polyester.Substantially uniform molecular weight distribution is particularlydesirable to produce a stabilized uniform dispersion with thedicyclopentadiene modified unsaturated polyester. Preferentiallyreacting dicarboxyl groups prior to reacting the monocarboxylic acid,produces a polymer having a relatively uniform molecular weightdistribution due to the degree of branching which is reasonablyuniformly produced by preferential reaction with the primary hydroxylson the polyol. Although not intending to be bound by theory, it isbelieved that the branched alkyd tends to solvate with styrene or vinyltoluene and similar monomer-solvents wherein swelling tends to occur inbranched areas which are dissimilar to the non-branched areas wheninteracting with the monomer. It is believed that the branching in thealkyd tends to set up stresses or internal forces between thenon-branched units whereupon negligible shrink occurs upon curing theunsaturated polyester system due to stress relieving and attendantmicrovoid development in the cured product. The branched alkyd of thisinvention interacts most efficiently with a dicyclopentadiene modifiedunsaturated polyester as hereafter set forth.

The branched, thermoplastic alkyd of this invention can be blended withdicyclopentadiene-modified polyester resin to produce an optically clearstabilized blend having no phase separation or visual incompatibility.The low shrink blend containing the fatty acid modified thermoplastic,branched alkyd was stable over extended periods of time of at leastabout 2 to 3 weeks. The stability of the alkyd of this invention incombination with the dicyclopentadiene modified unsaturated polyester isquite surprising in comparison with comparable alkyds such as soybeanoil alkyd and/or dehydroacetic acid alkyd. Many of the conventionalalkyds were either incompatible with unsaturated polyester and/orproduced high-shrinkage on molded parts as will become more apparent inthe examples.

Referring now to the dicyclopentadiene terminated unsaturated polyesterpolymer, the dicyclopentadiene terminated polyester polymer preferablycomprises a copolymer of glycol, unsaturated dibasic acid, and about0.1-0.4 mole of dicyclopentadiene per mole of unsaturated dibasic acid.Although all of the raw materials may be charged into the reactionvessel and reacted together at temperatures of 290°-310° F., it ispreferred that the dicyclopentadiene be preferentially esterified withthe unsaturated dibasic acid to minimize etherification with hydroxylgroups. At temperatures of about 308° F., etherification ofdicyclopentadiene with hydroxyl groups is a competing reaction toesterification of dicyclopentadiene with carboxyl groups. Hence,preferably only a portion of the glycol charge is reacted with a largemolar excess of dibasic unsaturated acid to first form primarily an acidterminated glycol-dibasic acid partial polymer. Thereafter,dicyclopentadiene is charged to the reactor to form a dicyclopentadieneesterified polyester prepolymer.

The preferred dicyclopentadiene-terminated polyester prepolymer isprepared by first charging into the reactor 2 molar equivalents ofdibasic unsaturated acid per molar equivalent of glycol. The glycol anddibasic acid mixture is then heated and reacted at temperatures of about290°-310° F. until substantially all of the glycol is esterified by theexcess molar equivalent of unsaturated dibasic acids. Completion of theglycol esterification may be measured by the acid number of thereactants becoming essentially constant, thus indicating no additionalhydroxyl groups are available for esterification. Thereafter,dicyclopentadiene is added to the reactor and reacted with theglycol-dibasic acid partial polymer at temperatures of less than 320°F., and preferably reaction temperatures of about 290°-310° F. After thedicyclopentadiene is completely charged to the reactor, the reactantmixture is maintained about 308° F. until the acid number of thereactants becomes essentially constant whereby the dicyclopentadiene ispreferentially esterified with available terminal acid groups of thepartial polymer. Thereafter, the remainder of the glycol charge may beadded to the reactor whereupon the reaction is continued at temperaturesof about 390° F. to complete the formation of adicyclopentadiene-terminated polyester polymer.

The glycols that can be used in synthesizing thedicyclopentadiene-terminated polyester polymer of this invention areconventional glycols and polyols and include, for example: ethyleneglycol, propylene glycol, diethylene glycol, dipropylene glycol,butanediol, hexanediol, pentaerythritol, triethylene glycol, trimethylolpropane, glycerol, or mixtures thereof. Preferably, the glycols used inthis invention are propylene glycol and/or dipropylene glycol as themajor glycol component.

The unsaturated dibasic acid components in the dicyclopentadienepolyester are alpha,beta-unsaturated dicarboxylic acids or anhydridesand include, for example: maleic, fumaric, mesaconic, itaconic,citraconic, and the like or mixtures thereof. The anhydrides arepreferred in the preparation of the dicyclopentadiene-esterifiedprepolymer. Similarly, unsaturated dicarboxylic acid may be reacted at308° F. with the dicyclopentadiene and thereafter esterified with thefull glycol requirement to produce a dicyclopentadiene-terminatedpolyester polymer. Although not preferred, lesser amounts of saturateddibasic acids or anhydrides may be introduced into the dicyclopentadienepolyester polymer to replace a portion of the unsaturated dicarboxylicacids. Conventional saturated dicarboxylic acids include, for example,orthophthalic anhydride or acid, terephthalic acid, isophthalic acid,adipic acid, sebacic acid, succinic acid, and the like acids oranhydrides. Similarly, minor amounts of multifunctional acid such astrimellitic anhydride can be incorporated into the dicyclopentadienepolyester backbone. The term dicarboxylic acid is intended to includedicarboxylic acid anhydrides.

Ethylenically unsaturated monomers copolymerizable with unsaturatedpolyester polymers are utilized to disperse or dissolve thedicyclopentadiene-terminated polyester polymer of this invention andform a dicyclopentadiene polyester resin mixture. Such ethylenicallyunsaturated monomers are well-known and include: styrene, methylstyrene, chlorostyrene, vinyl toluene, divinyl benzene, vinyl acetate,acrylic and methacrylic acid, lower alkyl esters of acrylic andmethacrylic acid, diallyl phthalate and like unsaturated monomers ormixtures thereof. For reasons of efficiency and economy, theethylenically unsaturated monomer most preferred in forming the lowprofile molding resin of this invention is styrene.

The foregoing stabilized resin dispersion desirably comprises by weighta mixture of at least about 25% of the dicyclopentadiene-terminatedpolyester polymer, about 5% to 20% of acid functional thermoplasticpolymer, and about 30% to 60% of styrene or other ethylenicallyunsaturated monomer. The preferred resin mixture contains at least about35 weight percent of said polyester, about 35% to 52% monomer, and about10% to 17% of an acid functional thermoplastic, branched alkyd polymerhaving an acid number of between about 5 to 35. The ratios of thepolyester, monomer and branched alkyd thermoplastic can be varied withinthe scope of this invention to provide a uniform and stabilized resindispersion system as hereinbefore described.

The low shrink molding resin composition of this invention is suitablefor mixing with additives known as chemical thickeners which arephysically mixed into the resin mixture of dicyclopentadiene polyesterpolymer, ethylenically unsaturated monomer, and thermoplastic polymer.The chemical thickeners generally include Group II metal oxides,hydroxides, and alkoxides. The oxides and hydroxides of alkaline earthsare preferred. For reasons of efficiency and economy, calcium oxide andmagnesium oxide, or the respective hydroxides, are most often employedwith low shrink molding compositions.

Catalysts and promoters often are incorporated in small amounts intothermosetting polyester resins containing ethylenically unsaturatedmonomer for curing the dicyclopentadiene polyester polymer and monomermixed with the thermoplastic polymer. Typical catalysts, for example,include organic peroxides and peracids such as tertiary butylperbenzoate, tertiary butyl peroctoate, benzoyl peroxide and the like.Examples of conventional promoters may be varied with the moldingprocess and similarly varied with the level and types of inhibitorsutilized, in a manner well-known in the art.

Fibers and fillers normally added to polyester molding resincompositions can be likewise used in formulating the molding compositionof this invention. Examples include: glass fibers, chopped fibers,chalk, kaolin, asbestos, diatomaceous earth calcium carbonate, talc,ceramic spheres, and quartz.

The following examples are provided to illustrate the preferredembodiments of this invention and are not intended to restrict the scopethereof. All parts are parts by weight, all percentages are expressed asweight percentages, and all temperatures are in degrees Fahrenheit,unless otherwise expressly specified.

EXAMPLE 1

The following raw materials were reacted to produce a branched fattyacid alkyd having an equivalent hydroxy functionality of 2.08:

.[.3216 grams.]. .Iadd.146.1 lbs. .Iaddend.adipic acid .Iadd.1.00 moles.Iaddend.

.[.2384 grams.]. .Iadd.70.1 lbs. .Iaddend.propylene glycol .Iadd.0.92moles .Iaddend.

.[.418 grams.]. .Iadd.10.7 lbs. .Iaddend.trimethylol propane .Iadd.0.08moles .Iaddend.

.[.246 grams.]. .Iadd.22.7 lbs. .Iaddend.stearic acid .Iadd.0.08 moles.Iaddend.

.[.6.26 grams dibutyl tin oxide..].

The propylene glycol, trimethylol propane, adipic acid and dibutyl tinoxide were charged to a reactor, upheated under N₂ blanket to about 310°F. whereupon water of reaction was drawn off. The reactant batch wasincreased in temperature gradually to 440° F. and held at 440° F. untilan Acid No. of about 50 was reached indicating that about 90% of thedicarboxylic groups were esterified. The stearic acid was then chargedlowering the batch temperatures to about 420° F. which was held until aGardner-Holt viscosity of W-X was obtained at 60% NVM in styrene. Thefinal Acid No. was 17. The polymer solid was thinned in inhibitedstyrene to provide a solution consisting of by weight about .[.50%.]..Iadd.60% .Iaddend.branched alkyd polymer and 40% styrene which wasmixed with the polyester of Example 2 to produce a low-shrink resin formolding low-profile parts.

EXAMPLE 2

A dicyclopentadiene modified polyester was synthesized from thefollowing raw materials:

9.9 gram moles of propylene glycol (752 grams)

2.0 gram moles of dicyclopentadiene (264 grams)

10.0 gram moles of maleic anhydride (980 grams)

Polymer synthesis was carried out in an ordinary reaction vesselsuitable for batch processing of polyesters and including an agitator,heating means, condenser, and inert gas flow.

FIRST STEP

Formation of an acid terminated partial copolymer of propyleneglycol-maleic ester was made by charging 5.0 gram moles of propyleneglycol and 10.0 moles of maleic anhydride together with 3% xylene (basedon the charge) into the reaction vessel and by heating under inert gasto 300° F. and holding at 300° F. for about 30 minutes until the acidnumber of the batch became constant. The acid number became constant at412 whereupon the second step commenced.

SECOND STEP

A prepolymer was prepared by adding the 2.0 moles of thedicyclopentadiene to the propylene-maleic partial copolymer at areaction temperature of 308° F. The 2.0 moles of dicyclopentadiene weremixed with 3% xylene and added to the reaction vessel at a steady andcontinuous rate for a time period of 30 minutes and the reaction thencontinued until the acid number of the batch leveled off at about 276.

THIRD STEP

A dicyclopentadiene-terminated polyester was prepared by charging theremaining 4.9 moles of propylene glycol to the foregoing prepolymer inthe reaction vessel, together with 0.3 grams of hydroquinone. The batchtemperature was gradually increased to about 390° F. and furtherprocessed until an acid number of 30 was reached. A test sample of 7parts resin mixed with 3 parts styrene yielded a viscosity of 3,600 cps.at 77° F. Xylene and water of reaction were stripped from the batch.

FOURTH STEP

The dicyclopentadiene-polyester polymer was then cooled to 200° F., 0.5grams of hydroquinone was added to the polymer which was then dilutedwith styrene to yield a dicyclopentadiene-polyester resin containing aratio of 70 weight parts of dicyclopentadiene-polyester polymer and 30weight parts of styrene monomer. Thereafter, about 1 gram ionol wasadded and the resin as discharged to a holding tank.

EXAMPLE 3

The resin composition of Example 1 was mixed at room temperature withthe resin composition of Example 2 by charging to a mixing vessel thefollowing:

20 weight parts of Example 1

64.3 weight parts of Example 2

15.7 weight parts of styrene.

The mixture was mildly agitated to form a uniform stabilized resindispersion system contains about 43% by weight styrene. The resultingresin had a viscosity of 450 centipoises, a weight per gallon of 8.9,and SPI gel time of 2 minutes, and SPI reaction time of 3 minutes, andan SPI reaction time of 3 minutes, and an SPI peak exothermic of 440° F.with 1% BPO at 180° F.

EXAMPLE 4

A bulk molding compound was prepared by mixing together in aBaker-Perkins dough mixer the following materials (parts by weight):

    ______________________________________                                        CaCO.sub.3       53.0                                                         Zinc Stearate    1.5                                                          Molding resin composition                                                      of Example 3    27.0                                                         t-Butyl Perbenzoate                                                                            0.5                                                          1/4" Glass Strand                                                                              20.0                                                         Mg(OH).sub.2     1.3                                                          ______________________________________                                    

The calcium carbonate and zinc stearate were first dry blended in themixer. Then the t-butyl perbenzoate catalyst was stirred into the liquidmolding resin composition and that mixture slowly added to the materialin the dough mixer while mixing continued. After thorough wetting of thecalcium carbonate had been achieved, the chopped glass fiberreinforcement was added and mixing was continued for about 2 minutesuntil the glass had been thoroughly wetted. The magnesium hydroxidethickener was then added and mixing continued for about two moreminutes. The mixing period after addition of the glass was kept as shortas possible, consistent with achieving wetting of the glass and uniformdispersion of the glass and thickener, so as not to cause excessivebreaking of the glass into shorter strands which would contribute lessreinforcement to the molded articles to be produced from the bulkmolding compound. The bulk molding compound was finally discharged fromthe mixer and held overnight (before molding) to insure that thethickening process was substantially complete.

EXAMPLE 5

A piece was molded in the following shape: about 9 inches square and 1/8inch thick having on one of its surfaces: (1) a straight rib about 1/2inch thick deep tapering from about 7-5/16 inches long and 9/16 incheswide at the base to about 7-3/16 inches long and 3/8 inches wide at itsflat outer extremity, having rounded ends and with its longitudinalcenterline about one inch from the edge of the nine-inch square; (2) anL-shaped rib about 1/2 inch deep with branches about one inch from theedges of the nine-inch square, the long branch being parallel to thestraight rib (1) above and near the opposite edge of the square, thewidth tapering from about 5/16 inches at the base to about 1/4 inch atits flat outer extremity and having round ends tapered at about the sameangle as the straight rib (1) above, and three circular bosses centeredat about 2 inch intervals along a line about 21/2 inches from the edgesof the square adjacent to the long branch of the L-shaped rib (2) aboveand being, respectively, (a) about 1/2 inch deep and tapering from aboutone inch in diameter at the base to about 15/16 inch at its flatextremity, and (c) about 1/4 inch deep and tapering from about 5/8 inchdiameter at the base to about 9/16 inch at its flat extremity, whereinall tapers were approximately flat except for 3 (c) in which the taperwas more pronounced near the base and less pronounced near theextremity.

About 350 grams of the bulk molding compound from Example 4 was placedas a compact mass in the steel die which had been preheated to 295° F.on the cavity side and 285° F. on the plunger side, the die was quicklyclosed in a press, and held closed for two minutes. The press was thenopened and the molded piece removed from the die.

EXAMPLE 6

Sheet molding compound was prepared by first mixing together, bysuccessive additions in the order stated, the following materials (partsby weight):

    ______________________________________                                        Molding resin composition                                                      of Example 3        100.0                                                    t-Butyl Perbenzoate  2.0                                                      Zinc Stearate        3.7                                                      CaCO.sub.3           180.0                                                    Mg(OH).sub.2         5.0                                                      1 inch hard glass strand                                                                           96.9                                                     ______________________________________                                    

The molding resin composition was introduced to a Cowles high speedmixer at about 1,000 rpm. The speed as gradually increased withsuccessive additions so as to maintain a vortex but without excessiveair entrainment, and the magnesium hydroxide thicknener was not addeduntil the previously added dry materials were thoroughly wetted anduniformly dispersed at which point the temperature was about 100° F.After addition of the magnesium hydroxide, stirring was continued forabout 2 minutes. This mixture was then discharged and promptly (beforeexcessive thickening, i.e. viscosity increase, had occurred) introducedinto a Brenner SMC machine wherein it was spread onto two sheets ofpolyethylene film to a thickness of about 1/16 inch on each sheet, theone inch glass strands distributed over the exposed surface of one ofthese sheets and the exposed surfaces of the two sheets then broughttogether by passing between a pair of rollers. Thorough wetting of theglass was accomplished by then passing the laminated sheet betweensuccessive sets of ridged rollers to provide a kneading action. Thesheet molding compound so produced was about 1/8 inch thick and was heldabout 5 days before molding so as to insure substantial completion ofthe thickening process.

EXAMPLE 7

A piece was molded in the molding die described in Example 5 from thesheet molding compound of Example 6 by folding a sheet of that materialweighing about 375 grams into the die cavity which had been preheated to300° F. on the cavity side and 290° F. on the plunger side. The die wasquickly closed in a press, held closed for about two minutes with anapplied pressure of about 1,000 lb/sq. in. (i.e. about 81,000 lbs. totalforce) and then released, the die opened, and the piece removed.

EXAMPLE 8

a. A molded part of Example 7 was measured for "sink marks" at the threecircular bosses which were particularly selected for exaggeratedwaviness. The molding of Example 7 produced an average deviation fromthe base line of 109 microinches which was measured by a BendixMicrocorder.

b. The molded part of Example 5 produced a deviation of 110 microinches.

c. A prior art resin (paraplex p-19C) was similarly compounded in themanner described in Examples 6 and as indicated in Example 7. Theaverage deviation was 140 microinches.

d. A standard polyester of 1.1 moles of propylene glycol, 0.5 moles ofmaleic anhydride, 0.5 moles of phthalic anhydride was cooked to acidnumber of 30 and reduced to 65% N.V.M. in styrene. The resin wascompounded similarly to composition of Example 6 and molded in the moldof Example 5 which produced a drastically deformed product. The sameresin composition was molded in an ordinary 0.10 inch thickness flatsheet which produced deviation in excess of 1,000 microinches.

e. Ordinary 24 gauge sheet steel was measured and found to have anaverage deviation of 275 microinches.

f. A sheet molding composition compounded as indicated in Example 6 wasmolded into a flat sheet having a thickness of 0.10 inches whichproduces negligible deviations.

EXAMPLE 9

A dicyclopentadiene-modified polyester polymer was synthesized in amanner similar to Example 1 from the following raw materials:

5.4 gram moles of propylene glycol

4.0 gram moles of dipropylene glycol

3.0 gram moles of dicyclopentadiene

10.0 gram moles of maleic anhydride.

The dicyclopentadiene polyester was compounded with the branched alkydthermoplastic in Example 1 and other components as indicated in Example4. An excellent low-shrink molding composition resulted and producedlow-profile molded parts.

EXAMPLE 10

A branched alkyd was produced in the manner indicated in Example 1 fromthe following raw materials.

3216 grams isophthalic acid

2384 grams dipropylene glycol

418 grams tall oil fatty acids

246 grams trimethylol propane

6.26 grams dibutyl tin oxide.

The raw materials (except for tall oil) were reacted in a first stageuntil at least sbout 75% of the dicarboxylic acid groups were reactedwhereupon the tall oil was added and the esterification completed. Thealkyd had a viscosity of W-Y at 60% NVM in styrene and an Acid No. of14.

The alkyd of this example was mixed with the DCP-polyester of Example 9together with addition styrene to provide a stabilized resin mixture byweight of 12% alkyd, 40% unsaturated DCP-polyester, and 48% styrene.Excellent low-profile molded parts were produced.

EXAMPLE 11

A branched alkyd similar to Example 1 was synthesized from the followingraw materials.

0.92 moles propylene glycol

0.08 moles glycerol

1.00 moles of adipic acid

0.08 moles of stearic acid

The propylene glycol, glycerol and adipic acid were charged to thereactor and reacted in the manner indicated in Example 1 until at leastabout 75% of the esterification reaction was completed whereupon thestearic acid was added and esterified. Esterification was continueduntil an Acid No. of 15 and a Gardner-Holt viscosity of W at 60% NVM instyrene. The alkyd was reduced in styrene as in Example 1.

This alkyd was mixed with the unsaturated polyester of Example 9together with additional styrene to provide a low-shrink resin systemcomprising by weight about 12% alkyd polymer, 40% unsaturated polyesterpolymer, and 48% styrene monomer. The low-shrink resin system was testedin the manner set forth in the foregoing examples. The resin systemproduced very good low-profile parts.

The foregoing examples are intended to be illustrative of this inventionbut not limiting except as defined in the appended claims.

What is claimed:
 1. In a low-profile molding resin composition forthickening with Group II metal oxides, hydroxides, or alkoxides, theresin system comprising by weight a mixture of (a) at least 25% of adicyclopentadiene terminated ethylenically unsaturated polyester polymerbeing the esterification product of an alpha, beta-ethylenicallyunsaturated dicarboxylic acid, dicyclopentadiene, and glycol, saiddicarboxylic acid esterified with about 0.1 to 0.4 moles ofdicyclopentadiene per mole of dicarboxylic acid, said polyester producedby first reacting a molar excess of said dicarboxylic acid with saidglycol to produce an acid terminated prepolymer and then reacting thedicyclopentadiene with said prepolymer, (b) about 5% to 20% of an acidfunctional thermoplastic polymer, and (c) about 30% to 60% of anethylenically unsaturated monomer, the improvement comprising:saidthermoplastic polymer being a fatty acid modified branched,thermoplastic alkyd condensation polymer, said alkyl being theesterification product of glycol and minor amounts of polyolpreferentially esterified with linear saturated dicarboxylic acidshaving between about 4 to 10 carbon atoms and monocarboxylic fatty acid,said alkyl containing between about 4% to 20% of said fatty acid byweight and having a hydroxyl equivalent branching functionality ofbetween about 2.02 and 2.2.
 2. The low-profile molding resin compositionof claim 1 wherein the linear dicarboxylic acid is selected from adipic,azelaic, and sebacic acids.
 3. The low-profile molding resin compositionof claim 1 wherein the monocarboxylic fatty acid is selected fromstearic, myristic, palmitic, and lauric acid.
 4. The low-profile moldingresin composition of claim 1 wherein the glycol and polyol arepreferentially esterified with at least about 75% of the dicarboxylicacid requirements prior to esterification with the monocarboxylic acid.